Automotive fuel, primarily gasoline, is a volatile liquid subject to potentially rapid evaporation, in response to diurnal variations in the ambient temperature. Thus, the fuel contained in automobile gas tanks presents a major source of potential evaporative emission of hydrocarbons into the atmosphere. Such emissions from a vehicle constitute what is technically called as ‘evaporative emissions’.
Industry's response to this potential issue has been the incorporation of the evaporative emission control systems (EVAP) into automobiles, to prevent fuel vapor from being discharged into the atmosphere. The EVAP systems include a fuel vapor storage canister containing adsorbent carbon that traps those fuel vapors and feeds them back to the intake manifold of the engine of the vehicle for combustion during canister purging operations, thus, reducing evaporative emissions from the vehicle.
Hybrid electric vehicles, including plug-in hybrid electric vehicles (PHEV's), pose a particular problem for effectively controlling evaporative emissions with this kind of system. Although hybrid vehicles have been proposed and introduced having a number of forms, these designs share the characteristic of providing a combustion engine as backup to an electric motor. Primary power is provided by the electric motor, and careful attention to charging cycles can result in an operating profile in which the engine is only run for short periods. Systems in which the engine is only operated once or twice every few weeks are not uncommon. Purging the carbon canister can only occur when the engine is running, and if the canister is not purged, the carbon pellets can become saturated, after which hydrocarbons will escape to the atmosphere, causing pollution.
Further, PHEVs have a sealed fuel tank designed to withstand differences in pressure and vacuum within the tank resulting from diurnal ambient temperature variations. As the fuel tank for PHEVs are sealed, diurnal and running loss vapors are contained in the fuel tank, and the canister is loaded primarily under conditions when the fuel tank is unsealed in order to refuel the tank. Subsequent to the canister being loaded from a refueling event, the canister may be purged of the fuel vapors, by a controller of the engine commanding a purge event at the subsequent drive cycle. Once the canister is clean of fuel vapors, it may thus stay clean until the next refueling event, which may be a considerable length of time if electric-only operation is primarily used.
For purging operations, some strategies utilize a “feed-forward” control strategy to maintain a stoichiometric air/fuel ratio for engine combustion. Such strategies may rely on a hydrocarbon sensor placed in a purge line between the canister and the engine, to measure a concentration of the vapor being purged from the canister. Based on the concentration, an engine fueling strategy may be controlled to reduce fuel injector pulses in order to maintain a stoichiometric air/fuel ratio during the purging event, thus reducing a risk of engine hesitation and/or engine stall as a result of the purge event. Thus, it is desirable for engine control strategies that it be known as to whether the hydrocarbon sensor is functioning as desired.
While the hydrocarbon sensor may be rationalized during a purging event by simply, indicating whether the hydrocarbon sensor responds to the fuel vapors being purged from the canister, after the canister is clean, it may be challenging to diagnose the hydrocarbon sensor until a subsequent refueling event. As discussed above, a subsequent refueling event may not take place for an extended time period under conditions where the vehicle is operated in the electric-only mode of operation, and as such, the hydrocarbon sensor may experience a long duration without being rationalized. During such time, if the hydrocarbon sensor becomes degraded, then a subsequent purge event may result in engine hesitation/stall, which may negatively impact customer satisfaction and which may lead to engine degradation over time. Thus, a method to diagnose the hydrocarbon sensor used for feed-forward air/fuel ratio control during purging of a fuel vapor storage canister, is desired.
The inventors have herein recognized the above-mentioned issues, and have developed systems and methods to address them. In one example, a method comprises routing blow-by gasses from a crankcase of an engine of a vehicle to an intake manifold of the engine, and then to a fuel vapor storage canister positioned in an evaporative emissions system of the vehicle, and indicating whether a hydrocarbon sensor used for feed-forward air/fuel ratio control during purging of the fuel vapor storage canister is functioning as desired based on a response of the hydrocarbon sensor during the routing. In this way, such a hydrocarbon sensor may be rationalized under conditions where the fuel vapor storage canister is clean, and where the vehicle is frequently operated in an electric-only mode of operation.
In one example, routing blow-by gasses may include a key-off condition following a drive cycle where the engine was in operation to propel the vehicle. Routing blow-by gasses to the intake manifold may further include opening a positive crankcase valve positioned in a line that coupled the crankcase to the intake manifold. In one example, the positive crankcase valve may comprise an electronically actuatable valve under the control of a controller of the vehicle, and may be commanded fully open to route blow-by gasses to the intake manifold. In another example, the positive crankcase valve may comprise a passively mechanically actuatable valve, controlled to a least restrictive position, such that blow-by gasses may be routed to the intake manifold.
By rationalizing the hydrocarbon sensor as described above and which will be further elaborated upon below, adverse situations such as engine hesitation and/or stall may be reduced or avoided in response to purging operations, which may in turn increase engine lifetime and customer satisfaction.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.